267 lines
10 KiB
Plaintext
267 lines
10 KiB
Plaintext
Generic Thermal Sysfs driver How To
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=========================
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Written by Sujith Thomas <sujith.thomas@intel.com>, Zhang Rui <rui.zhang@intel.com>
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Updated: 2 January 2008
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Copyright (c) 2008 Intel Corporation
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0. Introduction
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The generic thermal sysfs provides a set of interfaces for thermal zone devices (sensors)
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and thermal cooling devices (fan, processor...) to register with the thermal management
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solution and to be a part of it.
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This how-to focuses on enabling new thermal zone and cooling devices to participate
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in thermal management.
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This solution is platform independent and any type of thermal zone devices and
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cooling devices should be able to make use of the infrastructure.
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The main task of the thermal sysfs driver is to expose thermal zone attributes as well
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as cooling device attributes to the user space.
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An intelligent thermal management application can make decisions based on inputs
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from thermal zone attributes (the current temperature and trip point temperature)
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and throttle appropriate devices.
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[0-*] denotes any positive number starting from 0
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[1-*] denotes any positive number starting from 1
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1. thermal sysfs driver interface functions
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1.1 thermal zone device interface
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1.1.1 struct thermal_zone_device *thermal_zone_device_register(char *name, int trips,
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void *devdata, struct thermal_zone_device_ops *ops)
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This interface function adds a new thermal zone device (sensor) to
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/sys/class/thermal folder as thermal_zone[0-*].
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It tries to bind all the thermal cooling devices registered at the same time.
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name: the thermal zone name.
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trips: the total number of trip points this thermal zone supports.
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devdata: device private data
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ops: thermal zone device call-backs.
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.bind: bind the thermal zone device with a thermal cooling device.
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.unbind: unbind the thermal zone device with a thermal cooling device.
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.get_temp: get the current temperature of the thermal zone.
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.get_mode: get the current mode (user/kernel) of the thermal zone.
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"kernel" means thermal management is done in kernel.
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"user" will prevent kernel thermal driver actions upon trip points
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so that user applications can take charge of thermal management.
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.set_mode: set the mode (user/kernel) of the thermal zone.
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.get_trip_type: get the type of certain trip point.
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.get_trip_temp: get the temperature above which the certain trip point
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will be fired.
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1.1.2 void thermal_zone_device_unregister(struct thermal_zone_device *tz)
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This interface function removes the thermal zone device.
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It deletes the corresponding entry form /sys/class/thermal folder and unbind all
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the thermal cooling devices it uses.
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1.2 thermal cooling device interface
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1.2.1 struct thermal_cooling_device *thermal_cooling_device_register(char *name,
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void *devdata, struct thermal_cooling_device_ops *)
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This interface function adds a new thermal cooling device (fan/processor/...) to
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/sys/class/thermal/ folder as cooling_device[0-*].
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It tries to bind itself to all the thermal zone devices register at the same time.
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name: the cooling device name.
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devdata: device private data.
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ops: thermal cooling devices call-backs.
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.get_max_state: get the Maximum throttle state of the cooling device.
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.get_cur_state: get the Current throttle state of the cooling device.
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.set_cur_state: set the Current throttle state of the cooling device.
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1.2.2 void thermal_cooling_device_unregister(struct thermal_cooling_device *cdev)
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This interface function remove the thermal cooling device.
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It deletes the corresponding entry form /sys/class/thermal folder and unbind
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itself from all the thermal zone devices using it.
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1.3 interface for binding a thermal zone device with a thermal cooling device
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1.3.1 int thermal_zone_bind_cooling_device(struct thermal_zone_device *tz,
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int trip, struct thermal_cooling_device *cdev);
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This interface function bind a thermal cooling device to the certain trip point
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of a thermal zone device.
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This function is usually called in the thermal zone device .bind callback.
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tz: the thermal zone device
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cdev: thermal cooling device
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trip: indicates which trip point the cooling devices is associated with
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in this thermal zone.
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1.3.2 int thermal_zone_unbind_cooling_device(struct thermal_zone_device *tz,
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int trip, struct thermal_cooling_device *cdev);
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This interface function unbind a thermal cooling device from the certain trip point
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of a thermal zone device.
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This function is usually called in the thermal zone device .unbind callback.
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tz: the thermal zone device
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cdev: thermal cooling device
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trip: indicates which trip point the cooling devices is associated with
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in this thermal zone.
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2. sysfs attributes structure
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RO read only value
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RW read/write value
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Thermal sysfs attributes will be represented under /sys/class/thermal.
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Hwmon sysfs I/F extension is also available under /sys/class/hwmon
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if hwmon is compiled in or built as a module.
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Thermal zone device sys I/F, created once it's registered:
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/sys/class/thermal/thermal_zone[0-*]:
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|-----type: Type of the thermal zone
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|-----temp: Current temperature
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|-----mode: Working mode of the thermal zone
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|-----trip_point_[0-*]_temp: Trip point temperature
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|-----trip_point_[0-*]_type: Trip point type
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Thermal cooling device sys I/F, created once it's registered:
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/sys/class/thermal/cooling_device[0-*]:
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|-----type : Type of the cooling device(processor/fan/...)
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|-----max_state: Maximum cooling state of the cooling device
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|-----cur_state: Current cooling state of the cooling device
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These two dynamic attributes are created/removed in pairs.
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They represent the relationship between a thermal zone and its associated cooling device.
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They are created/removed for each
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thermal_zone_bind_cooling_device/thermal_zone_unbind_cooling_device successful execution.
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/sys/class/thermal/thermal_zone[0-*]
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|-----cdev[0-*]: The [0-*]th cooling device in the current thermal zone
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|-----cdev[0-*]_trip_point: Trip point that cdev[0-*] is associated with
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Besides the thermal zone device sysfs I/F and cooling device sysfs I/F,
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the generic thermal driver also creates a hwmon sysfs I/F for each _type_ of
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thermal zone device. E.g. the generic thermal driver registers one hwmon class device
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and build the associated hwmon sysfs I/F for all the registered ACPI thermal zones.
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/sys/class/hwmon/hwmon[0-*]:
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|-----name: The type of the thermal zone devices.
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|-----temp[1-*]_input: The current temperature of thermal zone [1-*].
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|-----temp[1-*]_critical: The critical trip point of thermal zone [1-*].
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Please read Documentation/hwmon/sysfs-interface for additional information.
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***************************
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* Thermal zone attributes *
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***************************
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type Strings which represent the thermal zone type.
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This is given by thermal zone driver as part of registration.
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Eg: "acpitz" indicates it's an ACPI thermal device.
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In order to keep it consistent with hwmon sys attribute,
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this should be a short, lowercase string,
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not containing spaces nor dashes.
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RO
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Required
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temp Current temperature as reported by thermal zone (sensor)
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Unit: millidegree Celsius
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RO
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Required
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mode One of the predefined values in [kernel, user]
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This file gives information about the algorithm
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that is currently managing the thermal zone.
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It can be either default kernel based algorithm
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or user space application.
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RW
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Optional
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kernel = Thermal management in kernel thermal zone driver.
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user = Preventing kernel thermal zone driver actions upon
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trip points so that user application can take full
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charge of the thermal management.
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trip_point_[0-*]_temp The temperature above which trip point will be fired
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Unit: millidegree Celsius
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RO
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Optional
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trip_point_[0-*]_type Strings which indicate the type of the trip point
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E.g. it can be one of critical, hot, passive,
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active[0-*] for ACPI thermal zone.
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RO
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Optional
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cdev[0-*] Sysfs link to the thermal cooling device node where the sys I/F
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for cooling device throttling control represents.
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RO
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Optional
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cdev[0-*]_trip_point The trip point with which cdev[0-*] is associated in this thermal zone
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-1 means the cooling device is not associated with any trip point.
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RO
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Optional
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******************************
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* Cooling device attributes *
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******************************
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type String which represents the type of device
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eg: For generic ACPI: this should be "Fan",
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"Processor" or "LCD"
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eg. For memory controller device on intel_menlow platform:
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this should be "Memory controller"
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RO
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Required
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max_state The maximum permissible cooling state of this cooling device.
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RO
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Required
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cur_state The current cooling state of this cooling device.
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the value can any integer numbers between 0 and max_state,
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cur_state == 0 means no cooling
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cur_state == max_state means the maximum cooling.
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RW
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Required
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3. A simple implementation
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ACPI thermal zone may support multiple trip points like critical/hot/passive/active.
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If an ACPI thermal zone supports critical, passive, active[0] and active[1] at the same time,
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it may register itself as a thermal_zone_device (thermal_zone1) with 4 trip points in all.
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It has one processor and one fan, which are both registered as thermal_cooling_device.
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If the processor is listed in _PSL method, and the fan is listed in _AL0 method,
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the sys I/F structure will be built like this:
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/sys/class/thermal:
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|thermal_zone1:
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|-----type: acpitz
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|-----temp: 37000
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|-----mode: kernel
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|-----trip_point_0_temp: 100000
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|-----trip_point_0_type: critical
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|-----trip_point_1_temp: 80000
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|-----trip_point_1_type: passive
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|-----trip_point_2_temp: 70000
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|-----trip_point_2_type: active0
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|-----trip_point_3_temp: 60000
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|-----trip_point_3_type: active1
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|-----cdev0: --->/sys/class/thermal/cooling_device0
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|-----cdev0_trip_point: 1 /* cdev0 can be used for passive */
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|-----cdev1: --->/sys/class/thermal/cooling_device3
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|-----cdev1_trip_point: 2 /* cdev1 can be used for active[0]*/
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|cooling_device0:
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|-----type: Processor
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|-----max_state: 8
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|-----cur_state: 0
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|cooling_device3:
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|-----type: Fan
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|-----max_state: 2
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|-----cur_state: 0
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/sys/class/hwmon:
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|hwmon0:
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|-----name: acpitz
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|-----temp1_input: 37000
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|-----temp1_crit: 100000
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